The present invention is related to a grinder, and more particularly to a grinder in which the rotary shaft can be fixed without using any tool for replacing the grinding disc.
A conventional pneumatic or electric grinder has a grinding disc mounted at bottom end for grinding or buffering a work piece. When grinding different work pieces, it is necessary to frequently replace the grinding disc.
In the conventional grinding structure, an eccentric rotary shaft is disposed at bottom end of the rotor (pneumatic grinder) or the motor (electric grinder). A hexagonal nut is fixed at bottom end of the rotary shaft. A worm is disposed at the center of the top face of the grinding disc. The worm is screwed in the nut, whereby the grinding disc is drivable by the rotary shaft. In addition, a protective sheath is disposed at bottom end of the grinder for covering the grinding disc and providing a protective effect.
The conventional grinder is equipped with a flat wrench. When replacing the grinding disc, the wrench is extended through the gap between the protective sheath and the grinding disc to fit onto the nut and prevent the rotary shaft from rotating. Under such circumstance, the grinding disc can be untightened or tightened. Such procedure is quite inconvenient, for the protective sheath obstructs the operator from seeing the nut. Therefore, it is hard for the operator to fit the wrench onto the nut. Moreover, the rotary shaft is eccentrically arranged and has unfixed position so that the operator often needs to try many times for wrenching the nut.
Furthermore, in case there is no tool available, it will be impossible to replace the grinding disc.